(1) Field of the Invention
This invention relates to a sealing glass composition for hermetically sealing two members, and, in particular, to such a composition for use in electronic parts production.
(2) Description of the Prior Art
In production of electronic parts such as semiconductor devices, fluorescent character display tubes, and others, sealing glass compositions have been used for sealing and/or bonding a plurality of members.
Generally speaking, the sealing glass composition is a powdery mixture comprising solder glass powder of a low melting temperature and refractory filler powder. As the solder glass, PbO-B.sub.2 O.sub.3 glass has been used which consists essentially of 40-90 wt % PbO and 8-15 wt % B.sub.2 O.sub.3.
Among various refractory oxides of a low thermal expansion used for the filler, lead titanate (PbTiO.sub.3) is conveniently used, especially for semiconductor devices, because it contains no alkali element. The use of lead titanate makes the thermal expansion coefficient of the sealing glass composition low and increases the flowability of the glass composition.
Japanese patent application laid open with publication No. 49-89713 discloses a sealing glass composition comprising a solder glass mixed with PbO-TiO.sub.2 crystal powder having a specific surface diameter of about 10 .mu.m or less. However, the sealing glass composition has a high thermal expansion coefficient of 54.5.times.10.sup.-7 /.degree.C., so that it is useless for bonding a silicon semiconductor chip (having a thermal expansion coefficient of about 32-35.times.10.sup.-7 /.degree.C.) and an alumina ceramic (having a thermal coefficient of about 70.times.10.sup.-7 /.degree.C.)
In order to lower the thermal expansion of the sealing glass composition, it is known in the art to use an increased amount of lead titanate or to use lead titanate powder of an increased particle size.
Another sealing glass composition comprising solder glass powder and fillers of lead titanate, zirconium silicate, and tin materials is disclosed in Japanese patent application laid open with publication No. 58-151374. The sealing composition has a sufficiently low thermal expansion coefficient and is useful for sealing semiconductor devices. However, the sealing glass composition has disadvantages because the lead titanate powder has an averaged particle size of about 15 .mu.m or more. It is difficult to deposit, by screen printing, a paste of the glass composition dissolved in a vehicle onto members to be bonded. Further, after sealing, microcracks are apt to cause in glass phase around the lead titanate crystals.